Resin-coated metal plate, metal can and can cap

ABSTRACT

A resin-coated metal sheet comprising a metal substrate and a thermoplastic resin layer formed on the surface of the metal substrate, wherein the thermoplastic resin layer comprises a polyester consisting chiefly of a polyethylene terephthalate and an ethylene polymer, and contains an ionomer resin as well as a tocopherol or a derivative thereof. The resin-coated metal sheet exhibits corrosion resistance, shock resistance (dent resistance) and resistance against high temperature and humidity, and withstands the retort-sterilization and the aging in a hot vendor or the like after the retort-sterilization.

TECHNICAL FIELD

[0001] The present invention relates to a resin-coated metal sheetobtained by laminating a film of a polyester composition on a metalsubstrate. More specifically, the invention relates to a resin-coatedmetal sheet having excellent shock resistance (dent resistance),resistance against high temperature and humidity, corrosion resistance,adhesiveness and workability, and to a metal can and a can closure madeby using the above resin-coated metal sheet having the above properties.

BACKGROUND ART

[0002] A side-seamless can has heretofore been produced by subjecting ametal blank such as an aluminum plate, a tin plate or a tin-free steelplate to at least one step of draw working between a drawing die and apunch to obtain a cup which includes a barrel without seam on the sidesurface thereof and a bottom integrally connected to the barrel withoutseam, and, as required, by subjecting the barrel to the ironing or tothe bend-elongation working to decrease the thickness of the side wall.

[0003] As a method of coating the side-seamless can with an organicfilm, there has been known a method of laminating a resin film on themetal blank prior to the molding. For example, Japanese UnexaminedPatent Publication (Kokai) No. 172556/1994 discloses laminating apolyester film having a limiting viscosity [η] of not smaller than 0.75on a metal.

[0004] It is an accepted practice to blend the polyester with anantioxidizing agent or a reforming component in order to improve theheat resistance and the shock resistance of the polyester used as aresin coating. For example, Japanese Unexamined Patent Publication(Kokai) No. 138387/1995 discloses a polyester film for lamination on ametal, comprising a polyester composition which contains anantioxidizing agent in an amount of from 0.01 to 5% by weight, andJapanese Unexamined Patent Publication (Kokai) No. 207039/1995 disclosesa polyester film for lamination on a metal sheet having a melting pointof from 120 to 260° C., and containing from 0.01% to 1% by weight of adiethylene glycol component and from 0.001 to 1% by weight of anantioxidizing agent.

[0005] The side-seamless can is produced by subjecting a resin-coatedmetal sheet which is obtained by coating in advance, a metal blank withan organic film, to the draw working or to the bend-elongation working.However, the organic coating on the inner surface is likely to bedamaged by a tool in the step of working. In the portions where thecoating is damaged, the metal is exposed actually or latently, andelutes out or corrodes from these portions. In producing the seamlesscans, there takes place a plastic flow in which the size increases inthe direction of height of the can and the size contracts in thecircumferential direction of the can. When the plastic flow takes place,the adhering force decreases between the surface of the metal and theorganic coating and, besides, the adhering force between the twodecreases with the passage of time due to residual strain in the organiccoating. Such a tendency becomes conspicuous particularly when thecontent is packaged while it is hot or when the canned content isheat-sterilized at a low temperature or at a high temperature.

[0006] Further, the dent resistance is a real shock resistance that isrequired for the canned products. This is such a property that theadhesiveness and coverage of the coating are still completely maintainedeven when the canned product is dented as represented by a mark of hitlike when the canned product is fallen or when the canned products comeinto collision with each other. That is, when the coating is peeled orwhen the coating develops pinholes or cracks in the denting test, theleakage occurs from these portions due to the elution of metal orpitting, and the content is no longer preserved. In general, thepolyester which exhibits excellent resistance against the content, lacksthe property of absorbing or relaxing the shock at the time of dentingtest, and imparting this property becomes an important assignment.

[0007] Further, the cans for packaging the content are usually printedon the outer peripheral surfaces thereof, and the polyester film isaffected by the heat of firing the printing ink. In practicallyproducing the cans, further, the cans are often heated in order tostabilize the resin coating by removing the strain therefrom. The effectof this heating upon the polyester is not negligible. The polyestertends to be thermally deteriorated, i.e., loses the molecular weight byheating accompanied by a decrease in the dent resistance, in theadhesiveness to the metal substrate, in the coating property, and in theworkability at the time of necking and wrap-seam working.

[0008] In order to improve the dent resistance after thermallydeteriorated at such high temperatures, Japanese Unexamined PatentPublication (Kokai) No. 19183/1998 discloses a resin layer applied ontoa metal substrate, i.e., discloses a laminate of a polyester or apolyester composition comprising:

[0009] a polyester segment derived from (I) a polyethylene terephthalatesegment and (II) a butylene glycol and an aromatic dibasic acid;

[0010] a polyester segment derived from (III) a butylene glycol and analiphatic dibasic acid; and

[0011] at least one non-sulfur antioxidizing agent having a molecularweight of not smaller than 400 in an amount of from 0.01 to 1.5 parts byweight per 100 parts by weight of the polyester or the polyestercomposition.

[0012] The can comprising the above-mentioned laminate exhibits markedlyimproved dent resistance after put to the thermal hysteresis at a hightemperature, but is not still capable of offering satisfactory corrosionresistance or shock resistance when placed under high temperature andhumidity conditions such as during the retort-sterilization or when putto the hot vendor.

[0013] Further, Japanese Unexamined Patent Publication (Kokai) No.195617/1995 discloses a resin-coated metal sheet having, on bothsurfaces or on one surface of a metal sheet, a film of a resincomposition comprising 1 to 25 parts by weight of an ionomer resin, and75 to 95 parts by weight of a saturated polyester resin which is acompound derived from a dicarboxylic acid and a hydroxy compound and inwhich, when the dicarboxylic acid component is 100 mol %, thedicarboxylic acid component comprises 50 to 95 mol % of a terephthalicacid and 50 to 5 mol % of an isophthalic acid and/or an orthophthalicacid, and the dihydroxy component is chiefly an ethylene glycol. Thisresin-coated metal sheet exhibits excellent flavor-retaining propertyyet exhibiting excellent shock resistance and adhesiveness.

[0014] According to the above prior art, however, a particular polyesterresin must be prepared. Since the isophthalic acid is fairly expensive,therefore, it is desired to obtain a high degree of shock resistance andadhesiveness as well as flavor-retaining property even when a cheaplyavailable general-purpose polyester resin is used.

[0015] If the general-purpose polyester resin is blended with theionomer resin, further, there occurs a new technical assignment in thatlumps are formed due to coagulation of the ionomer resin.

[0016] It has further been desired to improve the adhesiveness of theresin coating layer onto the metal substrate and to improve theworkability to cope with the production of cans at high speeds. It isfurther an important technical assignment to improve the resistanceagainst high temperatures and humidity to cope with theretort-sterilization and the subsequent aging even when the content isacidic and is strongly corrosive, to improve the shock resistance afterthe retort-sterilization, and to improve the corrosion resistance afterthe retort-sterilization or after having received the shocks.

DISCLOSURE OF THE INVENTION

[0017] It is an object of the present invention to provide aresin-coated metal sheet having corrosion resistance, shock resistance(dent resistance) and resistance against high temperature and humidity,which is capable of withstanding the retort-sterilization and the agingin a hot vendor after the retort-sterilization.

[0018] It is another object of the present invention to provide aresin-coated metal sheet featuring improved film-forming property,excellent workability, and satisfying a flavor-retaining propertyrequired for the cans, by using a general-purpose polyester resin,exhibiting adhesiveness even without using the primer, and making itpossible to decrease the cost of production.

[0019] It is a further object of the present invention to provide metalcans and can closures having these properties.

[0020] According to the present invention, there is provided aresin-coated metal sheet comprising a metal substrate and athermoplastic resin layer formed on the surface of the metal substrate,wherein the thermoplastic resin layer comprises a polyester consistingchiefly of a polyethylene terephthalate and an ethylene polymer, andcontains a tocopherol or a derivative thereof in an amount of from 0.05to 3% by weight.

[0021] In the resin-coated metal sheet of the present invention, it isdesired that:

[0022] 1. The polyester and the ethylene polymer are contained at aweight ratio of from 95:5 to 50:50;

[0023] 2. The ethylene polymer contains an ionomer;

[0024] 3. The coated layer has a melt viscosity of from 2000 to 10,000centipoises at a temperature of 260° C. and at a shearing rate of 122sect, the thermoplastic polyester in the coated layer has an inherentviscosity (IV) in a range of from 0.6 to 1.5, and the ionomer resin inthe coated layer is existing as a dispersion phase having an averageparticle diameter of not larger than 5 μm;

[0025] 4. The ionomer resin in the coated layer contains zinc as a metalseed; and

[0026] 5. The coated layer is blended with a novolak resin of abifunctional phenol.

[0027] According to the present invention, further, there is provided ametal can which is so formed that the resin-coated metal sheet becomesthe inner surface of the can.

[0028] According to the present invention, further, there is provided ametal closure which is so formed that the resin-coated metal sheet is onthe inner surface side of the can.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a diagram illustrating the thermal degradation of atocopherol used in the present invention;

[0030]FIG. 2 is a diagram illustrating the effect of suppressing thescorching of tocopherol used in the present invention;

[0031]FIG. 3 is a diagram illustrating the effect of the tocopherol usedin the present invention upon the molecular weight of PET;

[0032]FIG. 4 is a diagram illustrating a sectional structure of aresin-coated metal sheet of the present invention; and

[0033]FIG. 5 is a diagram illustrating another sectional structure ofthe resin-coated metal sheet of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] In the resin-coated metal sheet of the present invention, animportance resides in that a polyester comprising chiefly a polyethyleneterephthalate is combined with an ethylene polymer, and this polyestercomposition is blended with a tocopherol or a derivative thereof in anamount of from 0.05 to 3% by weight to form a resin coating. Due tothis, the resin-coated metal sheet is imparted with excellent corrosionresistance, shock resistance and resistance against high temperature andhumidity. Even when the resin-coated metal sheet is placed under severeconditions such as of retort-sterilization or in a hot vendor, theabove-mentioned properties are maintained creating an important featureof the invention.

[0035] It has been known already that the tocopherol with which isblended the polyester composition of the polyester consisting chiefly ofa polyethylene terephthalate and an ethylene polymer, works as anantioxidizing agent to improve the dent resistance by preventing adecrease in the molecular weight that is caused by the degradation atthe time of heat-treating the polyester resin. When the polyestercomposition of the polyester consisting chiefly of a polyethyleneterephthalate and an ethylene polymer, is blended with the tocopherolaccording to the present invention, not only the dent resistance isimproved but also corrosion is prevented even in case the film iscracked under severe conditions of retort-sterilization and in the hotvendor. Namely, corrosion resistance is markedly improved, which is anew and unexpected effect.

[0036] That is, as will become obvious from the results of Examplesappearing later, when the can walls of the resin-coated metal sheets areput to the cross-cut testing, corrosion does not almost proceed in thecase of the can wall of the resin-coated metal sheet of the presentinvention, proving markedly improved corrosion resistance.

[0037] The tocopherol or a derivative thereof used in the presentinvention is little degraded and features excellent heat resistance aswill be understood from the fact that it is holding a weight of notsmaller than 80% at a temperature of 260 to 270° C. at which thepolyethylene terephthalate is worked as shown in FIG. 1. Therefore, thepolyethylene terephthalate which is blended with the tocopherol exhibitsits excellent effect. Besides, the tocopherol (vitamin E) poses no harmeven in case it elutes out into the content, and maintains excellentsanitary properties.

[0038] The ethylene polymer serving as a reforming agent with which thepolyester consisting chiefly of the polyethylene terephthalate isblended, works to improve the shock resistance of the polyester, toimprove adhesiveness to the metal sheet, to improve workability, andmakes it possible to form a homogeneous resin coating on the metalsheet. The ethylene polymer, however, tends to be scorched by heating.When the polyester is blended with the ethylene polymer alone, lumps areformed to hinder the formation of the film. By blending the polyestercomposition of the polyester consisting chiefly of the polyethyleneterephthalate and the ethylene polymer with the tocopherol in an amountof from 0.05 to 3% by weight as contemplated by the present invention,it is made possible to suppress the scorching of the ethylene polymerand to favorably form the film.

[0039] That is, as shown in FIG. 2, when the polyester obtained byblending the polyethylene terephthlate with 18% by weight of the ionomerresin as the ethylene polymer is compared with the polyester obtained byblending the polyethylene terephthalate with 18% by weight of theionomer resin and 0.5% by weight of the tocopherol, the frequency ofscorching of the polyester drastically decreases when the tocopherol isblended. This is attributed to that the tocopherol itself is oxidizedpreventing the ionomer from being oxidized.

[0040] In the present invention, too, the tocopherol serving as anantioxidizing agent effectively suppresses the drop of molecular weightof the polyethylene terephthalate that is caused by the thermaldegradation.

[0041] Referring to FIG. 3, when the polyester composition of thepolyethylene terephthalate and the ethylene polymer is heated whilechanging the amount of addition of tocopherol (molecular weight ofbefore being heated: 58000), a drop in the molecular weight issuppressed when the tocopherol is added in large amounts. Upon addingthe tocopherol in a predetermined amount as described above, it is madepossible to effectively prevent a drop in the molecular weight of thepolyester caused by the thermal degradation and to improve the dentresistance.

[0042] According to the present invention, it is necessary that thetocopherol or a derivative thereof is contained in the polyestercomposition in an amount of from 0.05 to 3% by weight and, particularly,from 0.1 to 2% by weight. When the amount is smaller than the aboverange, the above-mentioned excellent effect obtained from the tocopherolor the derivative thereof is not exhibited to a sufficient degree forthe polyester composition. When the amount is larger than the aboverange, on the other hand, the polyester is gelled, and the film losessmoothness, making it difficult to obtain a seamless can.

[0043] In the resin-coated metal sheet of the present invention,further, the ionomer resin is used as the ethylene polymer, the coatedlayer of resin has a melt viscosity of from 2000 to 10,000 centipoisesat a temperature of 260° C. and at a shearing rate of 122 sec⁻¹, thethermoplastic polyester in the coated layer has an inherent viscosity(IV) in a range of from 0.6 to 1.5, and the ionomer resin in the coatedlayer is existing as a dispersion phase having an average particlediameter of not larger than 5 μm.

[0044] In the resin-coated metal sheet, the ionomer resin is notcompatible with the thermoplastic polyester resin but coagulates in thepolyester resin and exists as a dispersion phase having an averageparticle diameter of not larger than 5 μm. Therefore, excellentproperties such as toughness and abrasion resistance of the ionomerresin are not lost but are exhibited in the coated resin. Even when ageneral-purpose polyester resin is used in combination as a matrix,therefore, it is allowed to impart the shock resistance (particularly,dent resistance), adhesiveness and corrosion resistance to thegeneral-purpose polyester resin which constitutes the matrix.

[0045] The present inventors have discovered through experiment that theparticle diameter of the dispersion phase of the ionomer resin takespart in the dent resistance as is obvious from the results of Examplesappearing later though the reason is not clear yet. That is, when theaverage particle diameter of the dispersion phase is smaller than 5 μm(Example 18), the average electric current by flat sheet dents thatrepresents the dent resistance is about 0.3 mA. When the averageparticle diameter is larger than 5 μm (Comparative Examples 7 and 8), onthe other hand, the average electric current is about 3.0 mA which is astriking decrease in the dent resistance.

[0046] In order to decrease the average particle diameter of thedispersion phase of the ionomer resin to be smaller than 5 μm, further,it is important that the inherent viscosity (IV) of the thermoplasticpolyester in the coated layer lies in a range of from 0.6 to 1.5 and,particularly, from 0.65 to 1.2. That is, when the inherent viscosity issmaller than the above-mentioned range, the ionomer resin is nothomogeneously dispersed in the polyester and the particle diameter ofthe dispersion becomes larger than the above-mentioned range. When theinherent viscosity is larger than the above-mentioned range, on theother hand, the effect, i.e., the dent resistance is not exhibited to asufficient degree despite the ionomer resin is dispersed in the coatedlayer.

[0047] Further, the inherent viscosity that lies within theabove-mentioned range is important from the standpoint of improvingcorrosion resistance after the retort-sterilization. That is, thepolyester such as the polyethylene terephthalate is deteriorated by thetreatment under the conditions of a high temperature and a high humidityafter the retorting being caused by the fact that the polyester ishydrolyzed and degraded under such conditions, and the thermalcrystallization is promoted by a reduction in the molecular weight. Uponconfining the inherent viscosity of the thermoplastic polyester resin inthe coated layer to lie within the above-mentioned range, however, it isallowed to improve the barrier property against the corrosive componentsafter retorting and to improve the mechanical properties thereby toimprove the corrosion resistance (retort resistance) after theretorting.

[0048] In order to suppress the average particle diameter of thedispersion phase of the ionomer resin to be not larger than 5 μm,further, it is important that the coated layer has a melt viscosity in arange of from 2000 to 10000 centipoises and, particularly, from 3000 to8000 centipoises at a temperature of 260° C. and at a shearing rate of122 sec⁻¹. That is, when the melt viscosity is smaller than theabove-mentioned range, the resin is not kneaded to a sufficient degree,the ionomer resin is not homogeneously dispersed, and the diameters ofthe dispersed particles become too large. Further, when the meltviscosity is larger than the above-mentioned range, the extrusioncharacteristics are deteriorated.

[0049] The fact that the melt viscosity lies within the above-mentionedrange is important from the standpoint of workability, dent resistance,film-forming property and, particularly, from the standpoint ofpreventing the formation of lumps. That is, when the melt viscosity issmaller than the above-mentioned range, the film-forming property isdeteriorated due to the formation of lumps and the dent resistance isnot exhibited to a sufficient degree. When the melt viscosity is notsmaller than the above-mentioned range, on the other hand, theworkability is deteriorated.

Polyester

[0050] According to the present invention, the polyester consistingchiefly of a polyethylene terephthalate can be preferably used. That is,the polyester consisting chiefly of a polyethylene terephthalate is theone in which not less than 50 mol % of the aromatic carboxylic acidcomponent is a terephthalic acid component and not less than 50% of thealcohol component consisting chiefly of an aliphatic diol is an ethyleneglycol component.

[0051] So far as the above-mentioned conditions are satisfied, thepolyester may be a homopolyester, a copolymerized polyester, or a blendof two or more kinds thereof.

[0052] As the carboxylic acid component other than the terephthalic acidcomponent, there can be exemplified isophthalic acid,naphthalenedicarboxylic acid, p-β-oxyethoxybenzoic acid,biphenyl-4,4′-dicarboxylic acid, diphenoxyethane-4,4′-dicarboxylic acid,5-sodiumsulfoisophthalic acid, hexahydroterephthalic acid, adipic acid,sebacic acid, trimellitic acid and pyromellitic acid.

[0053] As the alcohol component other than the ethylene glycol, on theother hand, there can be exemplified such alcohol components aspropylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol,diethylene glycol, triethylene glycol, cyclohexanedimethanol, bisphenolA ethylene oxide adduct, glycerol, trimethylolpropane, pentaerythritol,dipentaerythritol and sorbitan.

[0054] The polyester must have a molecular weight large enough forforming a film. It is desired that the polyester has an inherentviscosity [η] of not smaller than 0.5 and, particularly, in a range offrom 0.6 to 1.5 as measured by using a mixed solvent ofphenol/tetrachloroethane as a solvent from the standpoint of barrierproperty against the corrosive components and mechanical properties.

Ethylene Polymer

[0055] As the ethylene polymer which is a reforming agent for thepolyester of the present invention, there can be exemplified low-,medium- or high-density polyethylene, linear low-density polyethylene,linear ultralow-density polyethylene, ethylene-propylene copolymer,ethylene-butene-1 copolymer, ethylene-propylenebutene-1 copolymer,ethylene-vinyl acetate copolymer, ionically crosslinked olefin copolymer(ionomer) and ethylene-acrylic acid ester copolymer.

[0056] Among them, the ionomer resin that will be described below can bepreferably used.

Ionomer Resin

[0057] The ionomer resin is an ionic salt in which part or whole of thecarboxyl groups in the copolymer of an ethylene and an α,β-unsaturatedcarboxylic acid, is neutralized with metallic cations, and its physicalproperties are affected by the degree of neutralization, i.e., by theconcentration of ions. In general, the melt flow rate (hereinaftersimply referred to as MFR) of the ionomer resin is affected by theconcentration of ions, and decreases with an increase in theconcentration of ions. Further, the melting point is affected by theconcentration of the carboxyl groups and decreases with an increase inthe concentration of the carboxylic groups.

[0058] Therefore, though not limited thereto only, it is desired thatthe ionomer resin used in the present invention has the MFR of notlarger than 15 g/10 min. and, particularly, in a range of from 5 g/10min. to 0.5 g/10 min., and has a melting point of not higher than 100°and, particularly, in a range of from 97° C. to 80° C.

[0059] As the α,β-unsaturated carboxylic acid constituting the ionomerresin, there can be exemplified unsaturated carboxylic acid having 3 to8 carbon atoms or, concretely, acrylic acid, methacrylic acid, maleicacid, itaconic acid, maleic anhydride, monomethyl ester maleate andmonoethyl ester maleate.

[0060] As a preferred base polymer, in particular, there can beexemplified ethylene-(meth)acrylic acid copolymer andethylene-(meth)acrylic acid ester-(meth)acrylic acid copolymer.

[0061] As the metal ions for neutralizing the carboxyl group in thecopolymer of the ethylene and the α,β-unsaturated carboxylic acid, therecan be exemplified Na⁺, K⁺, Li⁺, Zn⁺, Z² ⁺, Mg²⁺, Ca²⁺, Co²⁺, Ni²⁺,Mn²⁺, Pb²⁺ and Cu²⁺. According to the present invention, the copolymerneutralized with zinc can be particularly preferably used owing to itslarge degree of crosslinking and small susceptibility to humidity.Further, the remaining carboxyl groups that are not neutralized withmetal ions may be partly esterified with a lower alcohol.

[0062] In the resin-coated metal sheet of the second embodiment of thepresent invention as described above, it is important that the ionomerresin is existing as a dispersion phase having an average particlediameter of not larger than 5 μm and, particularly, in a range of from0.1 to 3.0 μm in the polyester resin which is a matrix. When the ionomerresin dispersed in the polyester is dissolved with a solvent such asxylene, traces after the ionomer has eluted out can be observed througha microscope. Upon measuring the diameters of the traces, it is allowedto measure the particle diameter of the dispersion phase of the ionomerresin.

[0063] In the present invention, it is desired that the ratio of thepolyester and the ethylene polymer is in a range of from 95:5 to 50:50and, particularly, from 90:10 to 70:30. When the amount of the ethylenepolymer is smaller than the above range, the polyester may not bereformed with the ethylene polymer to a sufficient degree, i.e., shockresistance, adhesiveness to the metal sheet and workability of thepolyester may not be improved to a sufficient degree, and the resincoating may not be homogeneously formed on the metal sheet. When theamount of the ethylene polymer is larger than the above range, on theother hand, there may be formed lumps, gel and fisheyes, making itdifficult to form the resin-coating on the metal sheet maintaining aconstant thickness. Besides, pinholes may develop during the working.

[0064] It is desired that the ionomer resin used in the presentinvention contains a constituent unit derived from the ethylene in anamount of from 80 to 99 mol % and, preferably, from 85 to 96 mol % andcontains a constituent unit derived from the unsaturated carboxylic acidin an amount of from 1 to 20 mol % and, preferably, from 4 to 15 mol %.

Tocopherol and its Derivatives

[0065] The tocopherol (vitamin E) used in the present invention isrepresented by the following general formula (I),

[0066] Preferred examples include α-tocopherol represented by the aboveformula (1) in which R₁=R₂=R₃=CH₃, β-tocopherol of the above formula (1)in which R₁=R₃=CH₃, R₂=H, γ-tocopherol of the above formula (1) in whichR₂=R₃=CH₃, R₁=H, and δ-tocopherol of the above formula (1) in whichR₃=CH₃, R₁=R₂=H.

[0067] In the above formula (1), further, there may be substituted anyoptical isomer d- or 1- concerning the asymmetric carbon atom at thesecond position; i.e., there can be used either a natural compound(d-type tocopherol) or a synthetic compound (dl-type tocopherol). Amongthem, the α-tocopherol can be effectively used.

Novolak Resin of Bifunctional Phenol

[0068] In the present invention, it is desired to use a novolak resin(novolak-type phenol resin) of a bifunctional phenol as aresin-reforming agent. The polyester film blended with the novolak-typephenol resin maintains excellent adhesiveness and corrosion resistanceeven after subjected to severe mechanical working and heat treatment.This film further exhibits excellent resistance against hightemperatures and humidities even after the passage of time underhigh-temperature and humidity conditions of after theretort-sterilization. As described earlier, the polyester such as thepolyethylene terephthalate is deteriorated by the treatment under theconditions of a high temperature and a high humidity after the retortingbeing caused by the fact that the polyester is hydrolyzed and degradedunder such conditions, and the thermal crystallization is promoted by areduction in the molecular weight. Upon blending the polyester with asmall amount of phenol resin, however, it is allowed to suppress thedegradation of the polyester caused by the hydrolysis and to markedlysuppress the deterioration of the coated layer of resin.

[0069] The novolak-type phenol resin used in the present invention isobtained by a known method, i.e., by reacting phenols with aformaldehyde or a functional derivative thereof in the presence of anacidic catalyst and water.

[0070] Though there is no particular limitation on the phenols that areused, there are preferably used monocyclic and monovalent phenols and,particularly, bifunctional phenols represented by the following formula(1),

[0071] wherein R1 is a hydrogen atom, an alkyl group or an alkoxy grouphaving not more than 4 carbon atoms, and wherein two of three R1s arehydrogen atoms, and the remaining one is an alkyl group or an alkoxygroup, and R is a hydrogen atom or an alkyl group having not more than 4carbon atoms, such as o-cresol, p-cresol, p-tert butylphenol,p-phenylphenol, p-ethylphenol, 2,3-xylenol and 2,5-xylenol, which can beused in one kind or in two or more kinds as chief components.

[0072] On the other hand, the formaldehyde that is used for the reactionis the one that is generally available as a formaline solution. As thefunctional derivative of the formaldehyde, on the other hand, there canbe exemplified paraformaldehyde and trioxane.

[0073] As the acid catalyst, there can be used hydrochloric acid,sulfuric acid, phosphoric acid, toluenesulfonic acid, oxalic acid andlactic acid. Though there is no particular limitation, the formaldehydeis used for the phenols in an amount that has heretofore been used forthe production of the novolak resin, e.g., in an amount of from 0.8 to 1mol per mol of the phenols. The reaction is usually conducted by heatingthe reaction system while it is refluxed, and the formed resin is put tothe treatments such as dehydration, neutralization, washing andrefining, and is recovered as a solid resin component.

[0074] In the present invention, it is desired that the phenol resin isblended in an amount of from 0.05 to 25% by weight and, particularly,from 0.1 to 15% by weight per 100% by weight of the polyester. When theblending ratio of the phenol resin is smaller than the above range, theresistance against high temperature and humidity and the shockresistance are not improved to a sufficient degree as compared to whenthe blending ratio lies within the above range. When the blending ratioof the phenol resin exceeds the above range, on the other, theflavor-retaining property tends to be deteriorated.

[0075] According to the present invention, further, the polyestercomposition can be blended with known blending agents for resins, suchas anti-blocking agent like amorphous silica, pigment like titaniumdioxide, various antistatic agents and lubricants according to knownrecipe.

[0076] The polyester resin is blended with the ethylene polymer(particularly, ionomer resin) and, further, with a reforming agent suchas phenol resin or tocopherol by dry-blending or melt-blending dependingupon the properties of the ionomer resin. In the former case, the resinis mixed by using a blender, Henschel's mixer or super-mixer, and isdirectly supplied into a hopper of an extruder. In the latter case, theresin is kneaded by using a monoaxial or biaxial extruder, kneader orBumbury's mixer. In either one of these cases, the polyester and theionomer resin are finally blended together at a temperature not lowerthan the melting point of the polyester. It is further allowable toprepare a master butch containing the ionomer resin at a relatively highconcentration, and with which the polyester may be blended.

[0077] The coated layer of the blend of the polyester resin and theionomer resin must have been kneaded by the above-mentioned method so asto possess a melt viscosity of from 2000 to 10000 centipoises and,particularly, from 3000 to 8000 centipoises at a temperature of 260° C.and at a shearing rate of 122 sec⁻¹.

[0078] The thermoplastic polyester resin exhibits a viscosity thatdecreases drastically due to the thermal decomposition as it is kneaded.It is therefore important that the thermoplastic polyester resin isblended with the ionomer resin in such a manner that the melt viscosityof the coated layer lies within the above-mentioned range, so that thethermoplastic polyester resin in the coated layer maintains an inherentviscosity over a range of from 0.6 to 1.5, and that the ionomer resinpossesses an average particle diameter of not larger than 5 μm and ishomogeneously dispersed in the thermoplastic polyester resin.

Metal Sheet

[0079] As the metal sheet used in the present invention, there can beused a variety kinds of surface-treated steel plates and a light metalsheet such as of aluminum. As the surface-treated steel plate, there canbe used the one obtained by annealing a cold-rolled steel plate,subjecting it to a secondary cold rolling and, then, to one or two ormore kinds of surface treatments such as zinc plating, tin plating,nickel plating, electrolytic treatment with chromic acid and treatmentwith chromic acid. There can be further used an aluminum-coated steelplate which is plated with aluminum or obtained by rolling aluminum.

[0080] As the light metal sheet, there is used a so-called pure aluminumplate and an aluminum alloy plate.

[0081] The initial thickness of the metal sheet may differ dependingupon the kind of metal, use of the container or size of the container.Generally, however, the metal sheet has an initial thickness of from0.10 to 0.50 mm. Among them, the surface-treated steel plate may have athickness of from 0.10 to 0.30 mm and the light metal sheet may have athickness of from 0.15 to 0.40 mm.

Resin-coated Metal Sheet and its Preparation

[0082] In the resin-coated metal sheet of the present invention, thepolyester film formed on the metal substrate may a layer comprising theabove-mentioned polyester composition alone, or may be a layer of alaminate with at least another polyester layer. In the case of thelatter laminate, it is important that the polyester composition(hereinafter often simply referred to as polyester composition)containing the ethylene polymer and the tocopherol is at least presenton a side that comes into contact with the metal substrate from thestandpoint of corrosion resistance, resistance against high temperatureand humidity and shock resistance.

[0083]FIG. 4 is a diagram illustrating a sectional structure of theresin-coated metal sheet of the present invention. The resin-coatedmetal sheet 1 comprises a metal substrate 2, and a layer 3 of apolyester composition containing an ethylene polymer and a tocopherolformed on the side that becomes the inner surface when a container ismolded. A thermoplastic polyester layer 4 is formed on the outer surfaceof the container of the metal substrate 2. The polyester layer on theouter surface may comprise a polyester composition or any otherpolyester.

[0084] Referring to FIG. 5 illustrating another resin-coated metalsubstrate, a laminated resin layer 6 is formed on the inner surface ofthe container, including an underlying layer 3 of a polyestercomposition on the side that comes in contact with the metal substrateand a polyester surface layer 5. In other respects, the resin-coatedmetal substrate is the same as the one shown in FIG. 4.

[0085] In the present invention, it is desired that the polyester layerhas a thickness of from 1 to 60 μm and, particularly, from 2 to 40 μm asa whole from the standpoint of balance between protecting the metalsubstrate and the workability. In the case of the laminated layer, onthe other hand, it is desired that the layer of the polyestercomposition containing the ethylene polymer and the tocopherol and theother polyester layer have a thickness of from 1:40 to 40:1 and,particularly, from 1:20 to 20:1 from the standpoint of corrosionresistance and balance between the resistance against high temperatureand humidity and the shock resistance.

[0086] According to the present invention, the polyester layer can beformed on the metal substrate by any means such as extrusion coatingmethod, cast-film heat-adhesion method, or biaxially stretched filmheat-adhesion method.

[0087] In the case of the extrusion coating method, the extruders areused in a number corresponding to the kinds of resins, the polyester isextruded through a die and the metal substrate is extrusion-coated withthe polyester of a molten state so as to be heat-adhered thereon. Thepolyester composition is heat-adhered onto the metal substrate byutilizing the amount of heat possessed by the molten polyester layer andthe amount of heat possessed by the metal sheet. The metal sheet isheated usually at a temperature of from 90 to 290° C. and, particularly,from 100 to 280° C.

[0088] When the polyester film is to be used, it is molded by the T-diemethod or by the inflation film-forming method. There can be used anunstretched film obtained by the cast-molding method, i.e., by quicklyquenching the film that is extruded. There can be further used abiaxially stretched film obtained by biaxially stretching the filmsuccessively or simultaneously at a stretching temperature and, then,heat-setting the film after it has been stretched.

[0089] In the resin-coated metal sheet of the present invention, thepolyester film can be adhered to the metal blank with no primer layerbetween the polyester film and the metal blank. This, however, is not toexclude the provision of the primer layer but, as required, a knownprimer for adhesion can be provided. The primer for adhesion exhibitsexcellent adhesiveness to both the metal blank and the film. As theprimer coating material exhibiting excellent adhesiveness and corrosionresistance, there can be exemplified a phenol epoxy coating materialcomprising a bisphenol epoxy resin and a resol-type phenolaldehyde resinderived from various phenols and formaldehyde. In particular, there canbe exemplified a coating material containing the phenol resin and theepoxy resin at a weight ratio of from 50:50 to 1:99 and, particularly,from 40:60 to 5:95. The adhesive primer layer is usually formedmaintaining a thickness of from 0.01 to 10 μM. The adhesive primer layermay be formed on the metal blank in advance, or may be formed on thepolyester film.

Metal Can and its Production

[0090] The metal can using the resin-coated metal sheet of the presentinvention can be produced by any can-producing method so far as it ismade of the above-mentioned resin-coating metal sheet. The metal can maybe a three-piece can having a seam on the side surface but is usually aseamless can (two-piece can). The seamless can is produced by subjectingthe above-mentioned resin-coated metal sheet to widely known means suchas draw/redraw working, bend-elongation working (stretch working) basedon draw/redraw working, bend-elongation/ironing working based ondraw/redraw working, or draw/ironing working, in a manner that thepolyester composition of the resin-coated metal sheet becomes the insideof the can.

[0091] The metal can according to the present invention is produced bythe above-mentioned means. Preferably, the thickness of the side wallportion is decreased by the bend-elongation based on the redrawingand/or by the ironing.

[0092] As compared to the bottom portion, it is desired that thethickness of the side wall is decreased by the bend-elongation and/or bythe ironing to assume a thickness which is from 20 to 95% and,particularly, from 30 to 85% of the blank thickness of the resin-coatedmetal sheet.

[0093] When, for example, the bend-elongation based on the draw/redrawworking is employed, a pre-drawn cup is molded by drawing theresin-coated metal sheet at a drawing ratio in a range of from 1.1 to3.0, redrawing the cup by using a redrawing punch and a redrawing die ata drawing ratio in a range of from 1.5 to 5.0, and effectivelydecreasing the thickness by bend-elongating the can by setting theradius (Rd) of curvature of the working corner of the redrawing die tobe from 1 to 2.9 times and, particularly, from 1.5 to 2.9 times as largeas the thickness (tB) of the metal blank, eliminating a change in thethickness between the upper part and the lower part of the side wall,and evenly decreasing the thickness over the whole side wall.

[0094] In general, the thickness of the side wall of the barrel can bedecreased to be not larger than 80%, or not larger than 45% and,particularly, not larger than 50% of the blank thickness (tB).

[0095] In the above redraw working, further, the side wall can besubjected to the ironing by arranging an ironing unit behind thebend-elongation working unit of the redrawing die.

[0096] It is desired that the thickness reduction ratio RI as defined bythe following formula,

RI={(tB−tW)/tB}×100  (2)

[0097] wherein tB is a thickness of the blank, and tW is a thickness ofthe side wall, of from 20 to 95% and, particularly, from 30 to 85%, isaccomplished through the bend-elongation working and the ironing.

[0098] The can that is obtained is subjected to at least one stage ofheat treatment to remove residual strain in the film caused by theworking, to evaporate the lubricant used for the working from thesurfaces thereof, and to dry and cure the printing ink printed on thesurfaces. The container after the heat treatment is quickly cooled or isleft to cool and, then, as required, subjected to the necking of onestage or of a plurality of stages, followed by flanging to obtain a canfor wrap-seaming.

Can Closure and its Production

[0099] The can closure of the resin-coated metal sheet of the presentinvention can be produced by any conventional closure production methodso far as it is made of the above-mentioned resin-coated metal sheet.Generally, the invention is applied to easy-to-open closures of thestay-on-tub type and to easy-to-open closures of the fully opening type.

EXAMPLES

[0100] The invention will now be described by way of Examples.

Preparation of the Resin-coated Metal Sheet

[0101] In Examples 1 to 6, 12 to 17 and in Comparative Examples 1 to 6,the copolymerized or blended polyester resins shown in Table 1, and theethylene polymers shown in Table 2, as well as a tocopherol (IRGANOXE201 produced by Chiba Specialty Chemicals Co.) were mixed in advance byusing the Henschel's mixer to obtain compositions as shown in Table 3.The compositions were then pulverized by using a pin mill, thrown into abiaxial extruder and melt-kneaded therein, passed through a T-die so asto be extruded into films maintaining a thickness of 20 μm, which werethen cooled through a cooling roll and were taken up to obtain castfilms. Here, the temperature conditions were selected to be optimum foreach of the resins.

[0102] In Example 13, however, the resin shown in Table 3 was used as alower layer, the polyester resin B shown in Table 1 was used as thesurface layer, and a two-layer cast film was prepared having a surfacelayer of 5 μm thick and a lower layer of 15 μm thick by using twobiaxial extruders and a two-layer T-die.

[0103] In Examples 1 to 6, 12 to 15 and in Comparative Examples 1 to 4,the thus prepared cast films were heat-laminated on both surfaces of TFSsteel sheets (sheet thickness of 0.18 mm, amount of metal chromium of120 mg/m², amount of chromium oxide hydrate of 15 mg/m²), and wereimmediately cooled with water to obtain resin-coated metal sheets. Here,the temperature of the metal sheets of before being laminated was set tobe higher than the melting point of the polyester resin by 15° C. Thelamination was effected by maintaining the laminate roll at atemperature of 150° C. and by passing the sheet at a rate of 40 m/min.

[0104] In Example 16 and in Comparative Example 5, the resin-coatedmetal sheets were obtained in the same manner as in Examples 1 to 6, 12to 15 and as in Comparative Examples 1 to 4 but using the aluminum alloysheet (A3004H39) having a sheet thickness of 0.24 mm.

[0105] In Examples 17 and in Comparative Example 6, the resin-coatedmetal sheets were obtained in the same manner as in Examples 1 to 6, 12to 15 and as in Comparative Examples 1 to 4 but using the aluminum alloysheet (A5052H38) having a sheet thickness of 0.25 mm.

[0106] In Examples 7 to 11, resins (tocopherol was IRGANOX E217DFproduced by Chiba Specialty Chemicals Co.) of compositions shown inTable 3 were dry-blended on the TFS steel sheets (sheet thickness of0.18 mm, amount of metal chromium of 20 mg/M², amount of chromium oxidehydrate of 15 mg/M²) heated at 250° C., supplied to an extruder of adiameter of 65 mm equipped with an extrusion-lamination facility,melt-extruded maintaining a thickness of 20 μm and was laminated on onesurface of TFS which was the outer surface. Then, the same resincomponent was supplied into an extruder of a diameter of 65 mm equippedwith an extrusion-lamination facility, and was melt-extruded maintaininga thickness of 20 82 m and was laminated on the other surface which wasthe inner surface while heating the sheet at a temperature lower thanthe melting point of the resin by 30° C. thereby to obtain aresin-coated metal sheet.

[0107] In Example 18 and in Comparative Examples 7 to 11, the polyesterresins shown in Table 4 as first components, and the ionomer resinsshown in Table 5 as second components, were thrown into a biaxialextruder so as to obtain the compositions shown in Table 6, and weremelt-kneaded, passed through a T-die and were extruded maintaining athickness of 30 aim, and were cooled through a cooling roll to obtainfilms which were, then, taken up as cast films. Here, the temperatureconditions were selected to be optimum for each of the resins.

[0108] In Example 18, however, the tocopherol was added as a thirdcomponent in an amount of 1% by weight.

[0109] In Example 18 and in Comparative Examples 7 to 9, the thusprepared cast films were heat-laminated on both surfaces of TFS steelsheets (sheet thickness of 0.18 mm, amount of metal chromium of 120mg/m², amount of chromium oxide hydrate of 15 mg/m²), and wereimmediately cooled with water to obtain resin-coated metal sheets. Here,the temperature of the metal sheets of before being laminated was set tobe higher than the melting point of the polyester resin by 15° C. Thelamination was effected by maintaining the laminate roll at atemperature of 150° C. and by passing the sheet at a rate of 40 m/min.

[0110] Evaluation was conducted as described below.

[0111] In Examples 19 to 21 and in Comparative Example 12, thepolyethylene terephthalates modified with 5 mol % of isophthalic acid,as well as the ethylene copolymers of compositions shown in Table 7 anda tocopherol (IRGANOX E201 produced by Chiba Specialty Chemicals Co.)were mixed in advance by using the Henschel's mixer to obtaincompositions as shown in Table 8. The compositions were then pulverizedby using a pin mill, thrown into a biaxial extruder and melt-kneadedtherein, passed through a T-die so as to be extruded into a filmmaintaining a thickness of 20 μm, which were then cooled through acooling roll and were taken up to obtain cast films. Here, thetemperature conditions were selected to be optimum for each of theresins. Thereafter, the thus prepared cast films were heat-laminated onboth surfaces of TFS steel sheets (sheet thickness of 0.18 mm, amount ofmetal chromium of 120 mg/m², amount of chromium oxide hydrate of 15mg/m²), and were immediately cooled with water to obtain laminates.Here, the temperature of the metal sheets of before being laminated wasset to be higher than the melting point of the polyester resin by 15° C.The lamination was effected by maintaining the laminate roll at atemperature of 150° C. and by passing the sheet at a rate of 40 m/min.

Flat Sheet dent ERV Testing

[0112] The coated surface to be evaluated of the resin-coated metalsheet was brought into contact with a silicon rubber having a thicknessof 3 mm and a hardness of 50° at 5° C. under wet condition. A steel ballof a diameter of ⅝ inches was placed on the side opposite thereto withthe metal sheet sandwiched therebetween. A weight of 1 kg was fallenfrom a height of 40 mm to shock-stretch the metal sheet.

[0113] The degree of cracks in the resin film on the shocked portion wasmeasured with an electric current maintaining a voltage of 6.00 V. Theexposure of metal due to the shock was evaluated based on an average ofsix values.

[0114] The results of evaluation were represented by:

[0115] ◯: Average electric current<0.1 mA.

[0116] X: Average electric current>0.1 mA.

Adhesion Testing

[0117] The resin-coated metal sheet was rolled until the thickness was50% of the initial thickness, and was cut in a crossing manner by usinga cutter knife. A cellophane tape (24 mm manufactured by Nichiban Co.)was stuck on the cut portion and was peeled therefrom.

[0118] The resin film remaining after the cellophane tape has beenpeeled off was evaluated.

[0119] The results of evaluation were represented by;

[0120] ◯: The film was not peeled off.

[0121] X: The film was peeled off.

Cross-cut Testing

[0122] An upper part of the can wall measuring 3 cm×3 cm was cut outfrom the metal can that was obtained, cut in a crossing manner by usinga cutter knife, immersed in an aqueous solution containing 0.1% ofsodium chloride, and was left to stay therein at 50° C. for one week toobserve the corroded state. Peeling of the film off the cross-cutportion and the degree of corrosion under the film were evaluated.

[0123] The results of evaluation were represented by;

[0124] ◯: Peeling of film or corrosion under the film is smaller than 1mm.

[0125] X: Peeling of film or corrosion under the film is larger than 1mm.

Retort Testing

[0126] Distilled water was poured at 95° C., retort treatment wasconducted at 135° C. for 30 minutes, the temperature was returned toroom temperature and distilled water was drained off. In the case of themetal can, the inner surface of the can was observed and evaluated forits corrosion. In the case of the closure, the inner surface of theclosure was observed and evaluated for its corrosion.

[0127] The results of evaluation were represented by;

[0128] ◯: Corrosion was not observed at all.

[0129] X: Abnormal condition such as corrosion was observed.

Package Testing

[0130] The metal can was evaluated as described below. Namely, the canfilled with the Coke was laid and was left to stand still. A ball of adiameter of 65.5 mm weighing 1 kg was fallen on the can at an end on theside of the bottom of the neck-worked portion of the can on an axis atright angles with the direction of rolling the metal sheet at atemperature of 5° C. Then, the can was preserved at 37° C. for one yearand, then, the inner surface of the can was observed.

[0131] Further, the closure was evaluated as described below. Namely,the can filled with the Coke was preserved at 37° C. for one year and,then, the inner surface of the closure was observed.

Melt Viscosity

[0132] The metal was dissolved from the resin-coated metal sheet toisolate the film, followed by vacuum-drying for at least 24 hours toobtain a sample. The melt viscosity was measured at 260° C., 122 sec⁻¹by using a Capillograph (manufactured by Toyo Seiki Co.).

IV (Inherent Viscosity)

[0133] The metal was dissolved from the resin-coated metal sheet toisolate the film, followed by vacuum-drying for at least 24 hours toobtain a sample. 200±0.2 Milligrams of the sample was weighed, addedinto 20 ml of a mixed solvent of phenol and a 1,1,2,2-tetrachloroethaneat a weight ratio of 1:1, dissolved in an oil bath heated at 130° C. forabout 30 minutes with stirring, and was left to cool down to roomtemperature. The solution cooled down to room temperature was passedthrough a glass filter, and was poured into the Ubbelohde's viscometersecured in a water vessel maintained at 30±0.1° C. constant. After thetemperature has been stabilized, the falling time was measured threetimes. The results measured according to the above method wassubstituted for the following formula, and the calculated results wereregarded to be IVs (inherent viscosities).$\lbrack\eta\rbrack = {{\frac{{- 1} + \sqrt{1 + {4k^{\prime}\eta_{sp}}}}{2k^{\prime}C}\quad \eta_{sp}} = {\frac{\tau - \tau_{0}}{\tau_{0}}\quad {{wherein}:}}}$

[0134] [η]: IV (inherent viscosity, dl/g)

[0135] η_(Sp): specific viscosity

[0136] k′: Huggins' constant (=0.33)

[0137] C: concentration (g/dl)

[0138] τ: falling time of the solution (sec)

[0139] τ₀: falling time of the solvent (sec)

Diameter of the Dispersed Particles

[0140] The metal was dissolved from the resin-coated metal sheet toisolate the film, followed by vacuum-drying for at least 24 hours toobtain a sample which was then immersed in xylene (maintained at 60° C.)for one minute. Thereafter, the sample was dried in open air and thesurface thereof was observed by using a scanning electron microscope.The particle diameter was found by measuring the areas of particles in aphotograph, calculating the diameters corresponding to true circleshaving such areas for at least 100 or more arbitrary particles, andaveraging the results.

Can Denting Test

[0141] The metal can was retort-treated according to the same procedureas the retort corrosion testing, and was preserved in aconstant-temperature chamber maintained at 37° C. for one month. Then, asteel ball having a diameter of ⅝ inches was placed on the side wall,and a weight of 1 kg was fallen from a height of 40 mm to shock-stretchthe metal sheet. Thereafter, the distilled water was drained off, andthe degree of cracks in the resin coating on the shocked portion wasevaluated relying upon an electric current by applying a voltage of 6.00V to the shocked portion.

Examples 1 to 15

[0142] The obtained resin-coated metal sheets were put to the flat sheetdent ERV testing and to the adhesion testing. The results were as shownin Table 3. Every resin-coated metal sheet exhibited excellent dentresistance and adhesiveness.

[0143] A wax-type lubricant was applied to the resin-coated metal sheetsfrom which disks having a diameter of 166 mm were obtained by punchingto form shallow-draw-formed cups. The shallow-draw-formed cups were thensubjected to the redraw/ironing working to obtain deep-draw-ironed cups.

[0144] The deep-draw-formed cups possessed the following properties.Diameter of cup:  66 mm Height of cup: 128 mm Thickness of can wall tothe blank thickness: 65% Thickness of flange to the blank thickness: 77%

[0145] The deep-draw-ironed cups were subjected to the doming accordingto the customary manner and were heat-treated at 220° C. The cups were,then, left to cool, the edges of the opening thereof were trimmed, thecurved surfaces thereof were printed, baked and dried. The cups werethen subjected to the necking and flanging to obtain seamless cans for acontent of 350 g. No problem was involved during the formation.

[0146] The cans were subjected to the cross-cut testing, package testingand retort-treatment testing by being filled with distilled water.

[0147] Favorable results were obtained as shown in Table 3 withoutcorrosion in the cross-cut testing, without corrosion in the dentedportion in the package testing and without corrosion in the retorttesting. From these results, the seamless cans that were obtained wereevaluated to be excellently suited for preserving beverages.

Example 16

[0148] The obtained resin-coated metal sheet was put to the flat sheetdent ERV testing and to the adhesion testing. The results were as shownin Table 3. The resin-coated metal sheet exhibited excellent dentresistance and adhesiveness.

[0149] A wax-type lubricant was applied to the resin-coated metal sheetfrom which a disk having a diameter of 166 mm was obtained by punchingto form a shallow-draw-formed cup. The shallow-draw-formed cup was thensubjected to the redraw/ironing working to obtain a deep-draw-ironedcup.

[0150] The deep-draw-formed cup possessed the following properties.Diameter of cup:  66 mm Height of cup: 127 mm Thickness of can wall tothe blank thickness: 45% Thickness of flange to the blank thickness: 77%

[0151] The deep-draw-ironed cup was subjected to the doming according tothe customary manner and was heat-treated at 220° C. The cup was, then,left to cool, the edges of the opening thereof were trimmed, the curvedsurface thereof was printed, baked and dried. The cup was then subjectedto the necking and flanging to a obtain seamless can for a content of350 g. No problem was involved during the formation.

[0152] The can was subjected to the cross-cut testing, package testingand retort-treatment testing by being filled with distilled water.

[0153] Favorable results were obtained as shown in Table 3 withoutcorrosion in the cross-cut testing, without corrosion in the dentedportion in the package testing and without corrosion in the retorttesting. From these results, the seamless can that was obtained wasevaluated to be excellently suited for preserving beverages.

Example 17

[0154] The obtained resin-coated metal sheet was put to the flat sheetdent ERV testing and to the adhesion testing. The results were as shownin Table 3. The resin-coated metal sheet exhibited excellent dentresistance and adhesiveness.

[0155] From the resin-coated metal sheet was then obtained by punching aclosure having a diameter of 68.7 mm in such a manner that theresin-coated surface was on the inside of the closure. The outer surfaceof the closure was, then, subjected to the partially opened scoring(width of 22 mm, remaining thickness after scoring of 110 μm, scoringwidth of 20 μm), rivetting, and to which a tab for opening was attachedthereby to obtain an SOT closure. No problem was involved during theformation.

[0156] The package testing and retort resistance testing were conductedby using the thus obtained SOT closure. No corrosion was recognized, andthe closure was evaluated to be excellently used for the metal cans.

Comparative Examples 1 to 4

[0157] The obtained resin-coated metal sheets were put to the flat sheetdent ERV testing and to the adhesion testing. The results were as shownin Table 3. The corrosion resistance, dent resistance and adhesivenesswere inferior to those of Examples.

[0158] It was attempted to produce the seamless cans by using theseresin-coated metal sheets under the same conditions as those of Examples1 to 15. While deep-drawing the cups, however, the film was broken andpeeled off, and the seamless cans could not be obtained. Even if theycould be obtained, corrosion occurred in the cross-cut testing,corrosion developed in the package testing, and corrosion took place inthe retort testing. Because of these results, the obtained seamless canswere evaluated to be not suited for preserving beverages.

Comparative Example 5

[0159] The obtained resin-coated metal sheet was put to the flat sheetdent ERV testing and to the adhesion testing. The results were as shownin Table 3. The corrosion resistance, dent resistance and adhesivenesswere inferior to those of Examples.

[0160] It was attempted to produce the seamless cans by using theseresin-coated metal sheet under the same conditions as those of Example16. No problem was involved during the formation.

[0161] Then, the seamless can was put to the cross-cut testing, packagetesting and retort-treatment testing by being filled with distilledwater.

[0162] As shown in Table 3, corrosion occurred in the cross-cut testing,corrosion developed in the package testing, and corrosion took place inthe retort testing. Because of these results, the obtained seamless canwas evaluated to be not suited for preserving beverages.

Comparative Example 6

[0163] The obtained resin-coated metal sheet was put to the flat sheetdent ERV testing and to the adhesion testing. The results were as shownin Table 3. The adhesiveness was inferior to that of Examples.

[0164] It was attempted to produce the SOT closure in the same manner asin Example 17. As a result, the film cracked on the scored portion.Further, corrosion occurred in the package testing and in the retorttesting. The closure, therefore, was evaluated to be not suited for usewith the metal cans.

Example 18

[0165] The obtained resin-coated metal sheet was put to the flat sheetdent ERV testing. The results were as shown in Table 6. The resin-coatedmetal sheet exhibited excellent dent resistance.

[0166] A wax-type lubricant was applied to these resin-coated metalsheet from which a disk having a diameter of 140 mm was obtained bypunching followed by drawing to form a draw-formed cup. The draw-formedcup was then subjected to the bend-elongation/ironing working twice toobtain a seamless cup.

[0167] The seamless cup possessed the following properties. Diameter ofcup:  52 mm Height of cup: 141 mm Thickness of can wall to the blankthickness: 37% Thickness of a portion corresponding to the 69% flangewith respect to the blank thickness:

[0168] The seamless cup was subjected to the bottom-formation processingaccording to the customary manner and was beat-treated at 220° C. Thecup was, then, left to cool, the edges of the opening thereof weretrimmed, the curved surface thereof was printed, baked and dried. Thecup was then subjected to the necking and flanging to obtain a seamlesscan having a content of 250 ml. No problem was involved during theformation.

[0169] The can was subjected to the retort-treatment testing by beingfilled with distilled water and to the denting testing.

[0170] As shown in Table 6, no corrosion occurred in the retort testing.Further, good results were obtained in the denting testing. From theseresults, the seamless can was evaluated to be excellently used forpreserving beverages.

Comparative Examples 7 to 9

[0171] The obtained resin-coated metal sheets were put to the flat sheetdent ERV testing and to the adhesion testing. The results were as shownin Table 6. The dent resistance was inferior to that of Examples.

[0172] By using the resin-coated metal sheets, seamless cans wereproduced under the same conditions as in Example 18. No problem wasinvolved during the formation.

[0173] Then, the seamless cans were put to the retort testing by beingfilled with distilled water and to the denting testing.

[0174] As shown in Table 6, corrosion occurred in the retort testing.The results of the denting testing were inferior, either. Because ofthese results, the obtained seamless cans were evaluated to be notsuited for preserving beverages.

Comparative Example 10

[0175] It was attempted to form a film of a resin as shown in Table 6.Due to the torque over of the extruder, however, the film could not beformed. Therefore, the results could not be evaluated.

Examples 19 to 21

[0176] The obtained laminates were put to the flat sheet dent ERVtesting and to the adhesion testing. The results were as shown in Table8. Every laminate exhibited excellent dent resistance and adhesiveness.

[0177] A wax-type lubricant was applied to laminates from which diskshaving a diameter of 166 mm were obtained by punching to formshallow-draw-formed cups. The shallow-draw-formed cups were thensubjected to the redraw/ironing working to obtain deep-draw-ironed cups.

[0178] The deep-draw-formed cups possessed the following properties.Diameter of cup:  66 mm Height of cup: 128 mm Thickness of can wall tothe blank thickness: 65% Thickness of flange to the blank thickness: 77%

[0179] The deep-draw-ironed cups were subjected to the doming accordingto the customary manner and were heat-treated at 220° C. The cups were,then, left to cool, the edges of the openings thereof were trimmed, thecurved surfaces thereof were printed, baked and dried. The cups werethen subjected to the necking and flanging to obtain seamless cans for acontent of 350 g. No problem was involved during the formation.

[0180] The cans were subjected to the package testing andretort-treatment testing by being filled with distilled water.

[0181] Favorable results were obtained as shown in Table 8 withoutcorrosion in the dented portion in the package testing and withoutcorrosion in the retort testing. From these results, the obtainedseamless cans were evaluated to be excellently suited for preservingbeverages.

Comparative Example 12

[0182] The obtained laminate was put to the flat sheet dent ERV testingand to the adhesion testing. The results were as shown in Table 3. Thedent resistance and adhesiveness were inferior to those of Examples.

[0183] It was attempted to produce the seamless can by using thelaminate under the same conditions as those of Examples 19 to 21. Whiledeep-drawing the cups, however, the film was peeled off, and theseamless can was not obtained and could not be evaluated. TABLE 1(Polyester resins) Polyester 1 Polyester 2 Blending Ratio of Ratio ofratio of copolymeri- copolymeri- polyester 1/ Name of Copolymerizablezation Copolymerizable zation polyester 2 composition component (mol %)component (mol %) (weight ratio) A none 0 B isophtharic acid 5 Cisophtharic acid 15 D none 0 naphthalene 92 80/20 dicarboxylic acid Ecyclohexane 5 dimethanol

[0184] TABLE 2 (Ethylene polymers) Name of Trade name and compositionKind grade Manufacturer A ionomer Himilan #1557 Mitsui-du PontPolychemicals Co. B ionomer Himilan #1707 Mitsui-du Pont PolychemicalsCo. C ethylene/methacrylic Nukrel N1108C Mitsui-du Pont PolychemicalsCo. acid copolymer D ethylene/acrylic Primacol #3330 Dow Chemical NihonCo. acid copolymer E ethylene/methyl Akrift WK307 Sumitomo Kagaku KogyoCo. methacrylate copolymer F ethylene/octene-1 Affinity PL1840 DowChemical Nihon Co. copolymer

[0185] TABLE 3 (Resin-coated metal sheets and evaluation) Ethylene Toco-Flat Cross- Polyester polymer pherol sheet cut Package Retrot AmountAmount Amount dent test test test (% by (% by (% by Sub- ERV Adhe-Moldability Corro- corro- corro- Kind wt.) Kind wt.) wt.) strate testsion Object Result sion sion sion Ex.1 A 80 A 19.9 0.1 TFS ◯ ◯ can good◯ no no Ex.2 A 80 A 19.0 1.0 TFS ◯ ◯ can good ◯ no no Ex.3 A 80 A 18.51.5 TFS ◯ ◯ can good ◯ no no Ex.4 A 80 A 17.5 2.5 TFS ◯ ◯ can good ◯ nono Ex.5 A 90 A 9.0 1.0 TFS ◯ ◯ can good ◯ no no Ex.6 A 60 A 39.0 1.0 TFS◯ ◯ can good ◯ no no Ex.7 A 80 B 19.0 1.0 TFS ◯ ◯ can good ◯ no no Ex.8A 80 C 19.0 1.0 TFS ◯ ◯ can good ◯ no no Ex.9 A 80 D 19.0 1.0 TFS ◯ ◯can good ◯ no no Ex.10 A 80 A/ 19.0 1.0 TFS ◯ ◯ can good ◯ no no E = 1/1blend (wt ratio) Ex.11 A 80 A/F = 19.0 1.0 TFS ◯ ◯ can good ◯ no no 1/1blend (wt ratio) Ex.12 B 80 A 19.0 1.0 TFS ◯ ◯ can good ◯ no no Ex.13 C80 A 19.0 1.0 TFS ◯ ◯ can good ◯ no no Ex.14 D 80 A 19.0 1.0 TFS ◯ ◯ cangood ◯ no no Ex.15 E 80 A 19.0 1.0 TFS ◯ ◯ can good ◯ no no Ex.16 B 80 A19.0 1.0 Al ◯ ◯ can good ◯ no no Ex.17 B 80 A 19.0 1.0 Al ◯ ◯ bottlegood — no no C.Ex.1 A 80 A 20.0 0.0 TFS ◯ X can good X corroded corrodedC.Ex.2 A 80 A 16.5 3.5 TFS ◯ X can good X corroded corroded C.Ex.3 A 99A 0.0 1.0 TFS X X can broken — — — C.Ex.4 A 45 A 54.0 1.0 TFS ◯ X canbroken — — — C.Ex.5 B 80 A 20.0 0.0 Al ◯ X can good X corroded corrodedC.Ex.6 B 80 A 20.0 0.0 Al ◯ X bottle cracked — corroded corroded

[0186] TABLE 4 (Polyester resin) Name of Inherent Copolymerizable Ratioof composition viscosity component copolymerization A 0.58 none 0 B 0.72none 0 C 0.85 none 0 D 0.90 isophthalic acid 5 E 1.55 none 0

[0187] TABLE 5 (Ionomer resin) Name of composition Melt flow rateMelting point A 0.9 88 B 5.0 91 C 14.0 90

[0188] TABLE 6 (Coated resin) Diameter Ionomer Melt of Film- Flat CanAmount viscos- dispersed forming sheet Retort dent- Poly- (% by IV ityparticles proper- dent resist- ing ester Kind (wt.) (dl/g) (poise) (μm)ty (mA) ance (mA) Remarks Ex.18 D B 15 0.80 6200 0.7 ◯ <0.1  ◯ 0.1 1 wt% tocopheral added Comp. A A 5 0.55 1700 5.8 X 2.3 X 3.3 Ex.7 Comp. A C15 0.53 1500 8.7 X 3.1 X 3.7 Ex.8 Comp. B — 0 0.69 4300 — X 3.5 X 5.1Ex.9 Comp. E — 0 — — — — — — — torque Ex.10 over of extruder

[0189] TABLE 7 (Ethylene polymers) Melt Name of flow composition KindGrade rate Manufacturer A ionomer Himilan #1706 0.9 Mitsui-du PontPolychemicals Co. B ethylene/butene EBM 2021P 1.3 Nihon Gosei copolymerGomu Co.

[0190] TABLE 8 Poly- Tocoph- Flat Cross- ester Ethylene Ethylene erolsheet cut Package Retort Amount polymer A polymer B Amount dent testtest test (% by Amount Amount (% by Sub- ERV Adhe- Moldability corro-corro- corro- wt) (% by wt) (% by wt) wt) strate test sion Object Resultsion sion sion Ex.19 80 10 10 0.5 TFS ◯ ◯ can good ◯ no no Ex.20 95 1.04.0 0.5 TFS ◯ ◯ can good ◯ no no Ex.21 50 25 25 0.5 TFS ◯ ◯ can good ◯no no Comp. 40 50 10 0.5 TFS X X can peeled — — — Ex.12

1. A resin-coated metal sheet comprising a metal substrate and athermoplastic resin layer formed on the surface of said metal substrate,wherein said thermoplastic resin layer comprises a polyester consistingchiefly of a polyethylene terephthalate and an ethylene polymer, andcontains a tocopherol or a derivative thereof in an amount of from 0.05to 3% by weight.
 2. A resin-coated metal sheet according to claim 1,wherein said polyester and said ethylene polymer are contained at aweight ratio of from 95:5 to 50:50.
 3. A resin-coated metal sheetaccording to claim 1 or 2, wherein said resin layer has a melt viscosityof from 2000 to 10,000 centipoises at a temperature of 260° C. and at ashearing rate of 122 sec⁻¹, and the polyester in the resin layer has aninherent viscosity (IV) in a range of from 0.6 to 1.5.
 4. A resin-coatedmetal sheet according to any one of claims 1 3, wherein the ethylenepolymer contains an ionomer resin.
 5. A resin-coated metal sheetaccording to claim 4, wherein the ionomer resin in said resin layer isexisting as a dispersion phase having an average particle diameter ofnot larger than 5 μm.
 6. A resin-coated metal sheet according to claim4, wherein the ionomer resin in said resin layer contains zinc as ametal seed.
 7. A resin-coated metal can obtained by molding aresin-coated metal sheet of any one of claims 1 to 6 in such a mannerthat the coated layer becomes the inner surface of the can.
 8. Aresin-coated metal closure obtained by molding a resin-coated metalsheet of any one of claims 1 to 7 in such a manner that the coated layerbecomes the inner surface of the can closure.